The California Title 24 solar energy code requires all new residential, commercial and multi-family constructions to have a solar system, barring a few exceptions. Below are a few simple calculators that would help you calculate the minimum solar size as required by the Title 24 code and also a list of exceptions that the code allows.
Single Family or ADU Solar Size Calculator
This calculator applies to single-family residences and ADUs that are new construction.
If you are unsure whether your ADU counts as new construction (vs. addition/alteration/conversion), please read our blog.
Equation – Title 24 Section 150.1-C
Annual Photovoltaic Electrical Output
kWPV = (CFA × A) / 1000 + (NDU × B)
Where:
- kWPV = kWdc size of the PV system
- CFA = Conditioned floor area (sq ft)
- NDU = Number of dwelling units
- A = CFA adjustment factor (Table 150.1-C)
- B = Dwelling unit adjustment factor (Table 150.1-C)
Low-Rise Multi-Family Solar Size Calculator
Applies to low-rise multi-family projects (< 3 habitable stories) that are new construction.
Equation – Title 24 Section 170.2-C
Annual Photovoltaic Electrical Output
kWPV = (CFA × A) / 1000 + (NDU × B)
Where:
- kWPV = kWdc size of the PV system
- CFA = Conditioned floor area (sq ft)
- NDU = Number of dwelling units
- A = CFA adjustment factor (Table 170.2-T)
- B = Dwelling unit adjustment factor (Table 170.2-T)
Commercial & High-Rise Solar Size Calculator
Applies to commercial buildings, high-rise residential, and mixed-use projects that are new construction.
Equation – Title 24 Section 140.10-A
Photovoltaic Direct Current Size
kWPVdc = (CFA × A) / 1000
Where:
- kWPVdc = Size of the PV system in kW
- CFA = Conditioned floor area (sq ft)
- A = PV capacity factor (from Table 140.10-A, based on building type)
Exceptions to Solar Requirements
Some projects are exempt from Title 24’s mandatory solar PV requirements. Below are the key exceptions (summarized for clarity):
Residential Exceptions (Sections 150.1(c)14 and 170.2(f))
- Roof Orientation / Limited Area – No PV required if south/east/west-facing roof area < 80 sq ft.
- Small System Size – No PV required if calculated size < 1.8 kWdc.
- Structural Limitations – No PV required if roof design cannot meet ASCE 7-16 structural standards.
- Pre-2020 Approvals – Projects approved by planning before Jan 1, 2020, where shading or roof restrictions prevent PV.
- Battery Storage Reduction – PV size may be reduced by 25% if paired with qualifying storage (≥7.5 kWh, JA12-compliant).
Commercial & High-Rise Exceptions (Section 140.10(a))
- Low Roof Area – No PV if available SARA < 3% of CFA.
- Small System Size – No PV required if required system size < 4 kWdc.
- Insufficient Contiguous Roof Space – No PV if available area < 80 sq ft.
- Structural Limitations – No PV if the roof cannot meet ASCE 7-16 standards.
- No VNEM/Community Solar – Multi-tenant buildings in areas without these programs.
Always confirm exceptions with your local building department.
Final Note
This calculator is designed to help you quickly estimate the minimum solar PV size required by California Title 24 for your project.
For full compliance with Title 24, including energy modeling, documentation, and registration, work with a Certified Energy Analyst. We ensure your project meets code in the most cost-effective and practical way.
